Energy

Energy

January 2016

Energy yielding nutrients

The energy yielding nutrients are carbohydrate, lipid, and protein. Alcohol supplies energy, but does not provide any other nutritional value and therefore will not be discussed here. For nutrition purposes, “energy” is the term used for what is commonly called “calorie.” The energy from a nutrient is the amount of heat released when the nutrient is burned. In the US, energy is commonly denoted as calorie (kcal). There has been an attempt to switch to the use of joules, which is the international unit of measure for energy. However, like the attempt to implement the metric system in the US, the change to joules has been met with resistance.

To convert kjoules to calories: 1 calorie = 4.184 kJ. Then divide kJ by 4.184 in order to express kjoules as calories.

Energy is expressed as kcal per gram of a nutrient:

Nutrient

Kcal per gram

Carbohydrate

4

Protein

4

Lipid

9

If you know the number of grams of an energy yielding nutrient, the way to determine the total energy in a food is calculated like this:

Snickers: 4 mini

Grams

kcal per gram

Kcals supplied by the nutrient

Cabohydrate

25

x 4

100

Protein

2

x 4

8

Lipid

8

x 9

72

Total

180

This food has an energy distribution of 100 kcals from carbohydrate, 8 kcals from protein, and 72 kcals from lipid. In food labeling, the manufacturer is allowed to round the numbers. Therefore, if the calories for 4 mini Snickers added up to, say, 177, the nutrition label of this particular food item could indicate that it has a total of 180 or even 175.

Dividing the kcals supplied by the nutrient by the total number of kcals gives you the percentage of nutrients in the food. Therefore, this product would have:

Carbohydrate = 100/180 = 56%

Protein = 8/180 = 4%

Lipid = 72/180 = 40%

About Us

Mary M. Flynn, PhD, RD, LDN developed this website starting in October 2015. She is an Associate Professor of Medicine (Clinical) at Brown University and teaches courses in nutrition at Brown, and lectures on nutrition in the Albert Medical School.
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